[libcxx] [test] Fix testcases that fail on systems with 16 bit wchar_t

Don't decode a UTF-8 character that is out of range for a 16 bit
`wchar_t`.

Differential Revision: https://reviews.llvm.org/D118191
diff --git a/libcxx/test/libcxx/localization/locales/locale.convenience/conversions/conversions.string/ctor_move.pass.cpp b/libcxx/test/libcxx/localization/locales/locale.convenience/conversions/conversions.string/ctor_move.pass.cpp
index 8816227..db0c660 100644
--- a/libcxx/test/libcxx/localization/locales/locale.convenience/conversions/conversions.string/ctor_move.pass.cpp
+++ b/libcxx/test/libcxx/localization/locales/locale.convenience/conversions/conversions.string/ctor_move.pass.cpp
@@ -6,9 +6,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-// 'do_bytes' throws a std::range_error unexpectedly
-// XFAIL: LIBCXX-WINDOWS-FIXME, powerpc-ibm-aix
-
 // XFAIL: libcpp-has-no-wide-characters
 
 // UNSUPPORTED: c++03
@@ -32,9 +29,9 @@
     // create a converter and perform some conversions to generate some
     // interesting state.
     Myconv myconv;
-    myconv.from_bytes("\xF1\x80\x80\x83");
+    myconv.from_bytes("\xEF\xBF\xBD");
     const auto old_converted = myconv.converted();
-    assert(myconv.converted() == 4);
+    assert(myconv.converted() == 3);
     // move construct a new converter and make sure the state is the same.
     Myconv myconv2(std::move(myconv));
     assert(myconv2.converted() == old_converted);